New NSAID: First COX-2 Inhibitor for Horses Approved by FDA

A new option in equine pain relief marks progress in the development of safer non-steroidal anti-inflammatory drugs (NSAIDs) for horses. Firocoxib (trade name Equioxx), manufactured by Merial, is the first equine NSAID specifically targeting the cyclooxygenase-2 (COX-2) enzyme to be approved by the FDA, and it is the first new equine NSAID option for systemic administration since 1990. The drug was released June 11.

COX-2 causes inflammation and pain in the body, while the enzyme cyclooxygenase-1 (COX-1) is associated with beneficial functions, including production of the protective mucous lining of the stomach.

Traditional NSAIDs such as phenylbutazone (Bute) and flunixin (Banamine), inhibit both COX-1 and COX-2. These drugs are known to cause ulcers, gastrointestinal bleeding, and kidney damage with prolonged use or high doses. COX-2-inhibiting drugs, including firocoxib and the human drugs Vioxx (rofecoxib) and Celebrex (celecoxib), selectively inhibit production of the inflammation-causing COX-2 enzyme, leaving the COX-1 enzyme free to perform its protective functions in the gastrointestinal tract and kidneys.

"On the equine market we've got the standard old NSAIDs, Bute and Banamine," said Anthony Blikslager, DVM, PhD, associate professor of equine surgery at North Carolina State University's College of Veterinary Medicine. "They're very effective for the control of pain, so they have very good efficacy. But the trouble is, they could be safer.

"I would hope that using a COX-2 inhibitor--if they can show that it's as effective as Bute--would still be safer because even though horses have overlapping function of COX-1 and COX-2, as compared to other species, you would still be leaving one of the enzymes alone to maintain organ function," Blikslager said.

The firocoxib product released by Merial is FDA-approved as a treatment for equine osteoarthritis. According to FDA documents, a field trial directly compared the lameness, pain on manipulation, swelling, and range of motion of more than 250 horses with naturally occurring osteoarthritis treated with phenylbutazone or firocoxib for two weeks. Veterinarians examining client-owned horses reported improvement more frequently in the firocoxib group than in the phenylbutazone group in all categories except lameness (after 14 days, veterinarians replied that 83.6% of horses in the firocoxib group had improved in the lameness category, compared to 85.6% of the horses on Bute).

"It seems every bit as effective, if not more so, than more commonly used NSAIDs," said Rick Mitchell, DVM, of Fairfield Equine Associates in Newtown, Conn., who has clients' horses on Equioxx as part of an efficacy field trial for horses with osteoarthritis. "It's an effective analgesic--it definitely does reduce lameness scores significantly--by anywhere from one to two lameness grades, at least, on the scale of 0 to 5--and it seems to be relatively rapid in onset. Within a day or two there's an improvement in the horses. The advantage for me, as a practitioner, is that we have so much less concern of ulcer potential."

In one study detailed in FDA documents, 32 horses were given the recommended dose or three or five times the recommended dose of firocoxib daily for up to 42 days. According to Peter Hanson, DVM, PhD, Dipl. ACVS, executive director of pharmaceutical research and development projects at Merial, there were some erosions or mild ulcers on the lips and in the mouths of horses in all groups (including the control group) from normal grazing activity, but these erosions were noted more frequently in the intentionally overdosed horses. The overdosed horses were no more affected by gastrointestinal ulcers than the control group.

Although the current label claim on Equioxx is specific to the treatment of osteoarthritis, Hanson said research on other uses for the drug is planned.

"Other areas that we will be looking at include the potential for an injectable at some point, because if you have a horse that has colic or some other activity, oral products just don't work, and we'll also have to validate that it is a product that works well in controlling colic, because currently we don't have that data," Hanson said. "There will be other things we'll consider and be bringing forward."

Mitchell noted that Equioxx does come at a higher price than other NSAIDs, but said the added margin of safety is worth it.

"Frankly, for the safety and the health of the horse, and the reduced potential for ulcers, and, therefore, the likelihood that other medications would be less-needed, the expense is probably negligible," Mitchell said.

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